Synthesis, characterization and properties of novel aliphatic–aromatic polyamide/functional carbon nanotube nanocomposites via in situ polymerization
An effective approach relying on in situ direct polycondensation to synthesize polyamide grafted with functional carbon nanotube (PA–FCNT) has been reported and the properties of PA nanocomposites were studied in this paper. The oxidized carbon nanotube (CNT–COOH), which was modified by the treatment of CNTs with mixed concentrated sulfuric acid and nitric acid, were converted into amino-functionalized CNTs (FCNT) by the reaction between CNT–COOH and an excess amount of 1,2-diaminoethan. Then, the aromatic–aliphatic polyamide/FCNT nanocomposites (PA–FCNT) were synthesized by using in situ polycondensation. To prove the two types of grafted CNT (FCNT–sPA with the properties closer to CNT, and FCNT–lPA with the properties closer to the polymer), PA–FCNT had been separated simultaneously after in situ preparation of PA–FCNT nanocomposite. The grafting was confirmed by investigation of FCNT–sPA and FCNT–lPA structures by Fourier transform infrared spectra, thermogravimetric analysis (TGA), nuclear magnetic resonance and transmission electron microscopy and presence of FCNT and PA in both compounds were observed. The effect of FCNT and pristine CNT on the morphology, thermal stability and flammability of PA were studied by TEM, TGA and microscale combustion calorimeter (MCC). TGA analysis illustrated that the grafted FCNT significantly increased the thermal stability and slightly improved char residues of PA. MCC tests showed the incorporation of FCNT in the polyamide resulted in the significant reduction of the heat release rate and total heat release, indicating that the flammability of PA had been reduced greatly.